As the use of small portable electronic devices becomes universal, the development of new secondary batteries, such as nickel hydrogen batteries or lithium (Li) secondary batteries, is actively in progress. Li secondary batteries among them are batteries that use carbon such as graphite as an anode active material, an oxide containing Li as a cathode active material, and a non-aqueous solvent as an electrolyte. Since Li is a metal with a very high ionization tendency and enables high-voltage generation, the development of batteries with high energy density is in progress.
As the cathode active material, Li transition metal oxides containing Li are most commonly used. 90% or more of such Li transition metal oxides are layered Li transition metal oxides, such as cobalt-based Li transition metal oxides, nickel-based Li transition metal oxides, and ternary Li transition metal oxides in which cobalt, nickel, and manganese coexist.
Although the development of a so-called Li-rich (Li-rich-based) high-capacity cathode material for high voltage is recently in progress, the capacity of 250 mAh/g or more is possible only when the primary particle size is 200 nm or less, in which case, the specific surface area increases, making an actual application of the material in a battery difficult to realize.